Method for the removal of airborne molecular contaminants using oxygen and/or water gas mixtures

ABSTRACT

The present invention discloses a method for the removal of a number of molecular contaminants from surfaces within a device. A purge gas containing oxygen and/or water is introduced into the interior of the device, contacting at least a portion of the interior surfaces. A contaminated purge gas is produced by transferring a portion of the contamination from the interior surfaces into the purge gas. The contaminated purge gas is removed from the device and the process is continued until the contaminant concentration in the contaminated purge gas is below a predetermined level.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.10/683,903, filed Oct. 10, 2003, which claims the benefit of U.S.Provisional Application No. 60/475,145, filed on Jun. 2, 2003. Thisapplication is also a continuation-in-part of U.S. application Ser. No.10/683,904, filed Oct. 10, 2003, which claims the benefit of U.S.Provisional Application No. 60/475,145, filed on Jun. 2, 2003. Theentire teachings of the above applications are incorporated herein byreference.

BACKGROUND OF THE INVENTION

In the manufacture of high purity products, such as silicon wafers,intended for semiconductor substrates or in the photolithography stepsof manufacture of semiconductors, it is necessary to maintain a highdegree of cleanliness. The products themselves must be clean, theatmospheres surrounding them throughout the manufacturing process mustbe clean, and the steps and equipment used in the manufacture must notimpair cleanliness. It is well known that with the minute sizes ofcircuitry and components incorporated into semiconductor chips, evenextremely small contaminant particles when deposited on chip surfacesare destructive to the chips. It is common for loss rates of wafers andchips during manufacturing to be a significant portion of the totalproduction due to system contamination.

Manufacturers of wafers and chips have been engaged in extensive andcontinual efforts to improve on the cleanliness of their fabricationfacilities (“fabs”) including efforts to have manufacturing and processmaterials and gases of high purity. Such efforts have been generallysuccessful in the past, in that gases with purities defined bycontaminant levels in the parts per million (ppm) and even into theparts per billion (ppb) ranges have been achieved. Generallyimprovements in process system cleanliness have paralleled increases inthe component density of chips and reductions in the size of chipcomponents and circuitry.

However, the ability of the prior art to achieve such parallelimprovements in gases has more recently been severely taxed as the sizeof chip components has continued to decrease and component density hascontinued to increase. With the movement to 198 nm and 157 nmsemiconductor technologies, the ability of the products to toleratecontamination has substantially decreased, and process gases thatpreviously were of adequate purities are no longer suitable. Scale-uptechniques that previously achieved adequate improvements in the purityof such gases have been found to be ineffective in these “ultra highpurity” (UHB) systems in which the lower nm level technologies areproduced. Further, at the lower IC dimensions materials that werepreviously considered minor contaminants have been found to act as majorcontaminants, and the prior art gases have been found to be ineffectivein removing such contaminant materials.

Ultrahigh purity products and process tools are susceptible to airbornemolecular contaminants (AMCs) that can reduce product quality and yield.AMCs generally include, but are not limited to SO_(x), NO_(x),siloxanes, organophosphorus compounds, ammonia, moisture, oxygen andhydrocarbons (>4 carbons). For purposes of the present invention, oxygenand moisture are not considered to be AMCs.

In the production of wafers for the semiconductor industry, there arethree major sources of contamination, wafer storage containers (forexample, Front-Opening Unified Pods or FOUPs) themselves; clean room airthat enters the container as the wafers are moved between tools and thewafers themselves that may leech contaminants during the variousmanufacturing processes. Methods have been developed to sufficientlyreduce water and oxygen contamination in the manufacturing process.Additionally, methods have been developed for the removal of reactionproducts of the wafer with water and oxygen (e.g., silicon oxides) thatcan form on the surface of the wafers. However, technologies have notdeveloped for the efficient removal of a number of airborne contaminantsand their resulting reaction products on wafers.

Various contaminants have different effects. For example, inphotolithography simple hydrocarbons can condense on the lens assemblyand result in transmission loss. Heavy hydrocarbons and significantconcentrations of light hydrocarbons irreversibly deposit on opticalsurfaces and become graphitized by ultraviolet (UV) exposure. In asimilar manner, silicon-containing organics, e.g., siloxanes, reactunder UV irradiation to produce SiO₂ crystallites that refract andabsorb the incident light. Other AMCs, e.g., NO_(x) and SOX_(x),typically wherein 0<x≦3, cause optical hazing. Basic AMCs, e.g., amines,quench the photoacids, in addition to causing optical hazing. In thecontext of photolithography, oxygen and water can be detrimental to theproduction process and are typically considered to be AMCs in the priorart. Recently, its has been reported by Veillerot et al., (Solid StatePhenomena Vol. 92, 2003, pp. 105-108) that atmospheric hydrocarboncontamination has a detrimental impact on 4.5 nm gate oxide integritywhen wafers are stored in a continuous flow of purge gas between gasoxide and polysilicon deposition steps.

Approaches being tried to reduce this contamination include large-scalechemical filtration of the cleanroom air, moving from open to closedcassettes, and nitrogen purging of wafers during storage and transport.Nitrogen purging of UHP components such as valves and gas deliverypiping, has been practiced for many years, and can be effective inremoving oxygen and water. However, large scale use of nitrogen forpurging large volume IC process equipment and large numbers of cassettescan be expensive and present a serious asphyxiation hazard.Additionally, it is suspected that nitrogen purging of hydrocarboncontaminated surfaces is not completely effective in removing thehydrocarbons.

Methods for analysis of contaminants in gas streams are well known. FIG.1 (Prior Art) is a schematic flow diagram of a double dilution system100 coupled to a gas chromatograph gas analysis system 120. The doubledilution system 100 comprising mass flow controllers 106, 108, 110, and112 enables the precise dilution of a gas standard 114 with a carriergas 102 over a range of six orders of magnitude (10⁶). Commonlyavailable gas standards in the part per million range can be effectivelydiluted to the part per trillion (ppt) range with system 100. Thedilution system 100 can be coupled to a gas chromatograph system 120 forthe purposes of calibrating the response of the chromatograph 126, byconnecting the output 116 of the dilution system to the input 122 of thechromatographic gas analysis system 120. A cold trap 124 accumulatescondensed hydrocarbons in the sample, prior to injection into the gaschromatograph 126. In this manner, the effective sensitivity of thechromatograph can be increased and ppt level hydrocarbon concentrationsreliably measured.

FIG. 2 (Prior Art) is a calibration graph 200 of signal response area204 versus sample hydrocarbon concentration 202 for various hydrocarbonmolecules including benzene 206, toluene 208, ethyl-benzene 210,meta,para-xylene 212, ortho-xylene 214, a second toluene 216, for theanalysis system 120 coupled to dilution system 100. The data 220 show alinear response relationship between the peak area 204 and concentration202 over almost six orders of magnitude, with a minimum sensitivity of 1ppt

FIG. 3 (Prior Art) is a graph 300 of time 302 versus gas chromatograph126 detector signal 304 for a sample containing 1 ppt each of benzene,toluene, ethyl-benzene, and xylene. Here it can be seen that 1 ppt levelconcentrations for each of the hydrocarbons in the mixture result inclearly distinguished peaks for benzene 306, toluene 308, ethyl-benzene310, and xylene 312.

SUMMARY OF THE INVENTION

The present invention is generally directed to a method for removingairborne molecular contaminants (AMC) from a surface comprisingcontacting at least a portion of the surface and the area surroundingthe surface with a purified purge gas, where the purge gas comprisesoxygen, water or a combination thereof, and the purified purge gas hasan AMC concentration less than about 1 part per billion (ppb) on avolume basis; producing a contaminated purge gas by transferring aportion of the contaminants from the surface into the purified purgegas; and removing the contaminated purge gas from the surface.

It is an object of the present invention to provide a method for theremoval of airborne molecular contaminants (AMCs) from surfaces,generally within a device. In one embodiment, the method comprisesintroducing a purge gas containing oxygen and preferably having an AMCconcentration of less than 1 part per billion on a volume basis into aninterior portion of the device, contacting at least a portion of thesurfaces with the purge gas, producing a contaminated purge gas bytransferring a portion of the molecular contaminants from the surfacesinto the purge gas, and removing the contaminated purge gas from thedevice. The preceding steps are typically continued or repeated untilthe contaminant concentration in the contaminated purge gas is decreasedto a desired level, preferably below 1 part per billion on a volumebasis, more preferably below 100 ppt contaminant on a volume basis.Additionally, the oxygen containing purge gas may further includemoisture (i.e., water).

In a further embodiment of the present invention, the method comprisespurifying a purge gas containing oxygen at a concentration between 1 and25 volume %, also preferably having a molecular contaminantconcentration of less than 1 ppb, introducing the purified purge gasinto an interior portion of the device, contacting at least a portion ofthe surfaces with the purified purge gas, producing a contaminated purgegas by transferring a portion of the molecular contaminants from thesurfaces into the purified purge gas, and removing the contaminatedpurge gas from said device. The method typically further comprisescontinuing the preceding steps until a contaminant concentration in thecontaminated purge gas is decreased to a desired level, preferably belowabout 1 ppb, more preferably below about 100 ppt. Additionally, theoxygen containing purge gas may contain water at a concentration betweenabout 100 ppm to about 2 volume %.

In a third embodiment of the present invention, the method comprisespurifying a purge gas containing water (e.g., at a concentration betweenabout 100 ppm and about 2 volume % moisture) with the overall mixturehaving a molecular contaminant concentration of less than 1 ppb,introducing the purified purge gas into an interior portion of thedevice, contacting at least a portion of the surfaces with the purifiedpurge gas, producing a contaminated purge gas by transferring a portionof the molecular contaminants from the surfaces into the purified purgegas, and removing the purified purge gas from said device. The methodtypically further comprises continuing the preceding steps until thecontaminant concentration in the contaminated purge gas is decreased toa desired level, preferably below about 1 ppb contaminant on a volumebasis, more preferably below about 100 ppt contaminant.

The methods disclosed herein are particularly useful for removingcontaminants from surfaces such as the interior surface of an ultrahighpurity gas line and the interior surface of valves present in a gasline, along with the interior surface of stainless steel chambers (e.g.chambers used for manufacturing silicon wafers).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram of a double dilution manifold coupledto a gas chromatograph gas analysis system.

FIG. 2 is a calibration graph for the apparatus of FIG. 1 showing signalresponse area versus sample hydrocarbon concentration for varioushydrocarbon molecules.

FIG. 3 is a graph of gas chromatograph detector signal versus time for asample containing 1 ppt each of various hydrocarbon components.

FIG. 4 is a schematic flow diagram of a testing setup according to anembodiment of the present invention.

FIG. 5 is a cross section schematic view of a wafer chamber according toan embodiment of the present invention.

FIG. 6 is a process block diagram of a first purging process accordingto an embodiment of the present invention.

FIG. 7 is a process block diagram of a second purging process accordingto an embodiment of the present invention.

FIG. 8 is a process block diagram of a third purging process accordingto an embodiment of the present invention.

FIG. 9 is a graph of hydrocarbon concentration versus time for two purgegas mixtures exiting the wafer chamber of FIG. 5, with no wafer in thechamber, according to an embodiment of the present invention.

FIG. 10 is a graph of hydrocarbon concentration versus time for twopurge gas mixtures exiting the wafer chamber of FIG. 5, with a siliconwafer in the chamber, according to an embodiment of the presentinvention.

FIG. 11 is an expanded version of FIG. 10, showing the time span from 10hrs to 25 hrs in greater detail, according to an embodiment of thepresent invention.

FIG. 12 is a graph of meta- and para-xylene concentration versus timefor three purge gas mixtures exiting the wafer chamber of FIG. 5, with asilicon wafer in the chamber, the purge gases containing 0%, 1%, and 20%oxygen, according to an embodiment of the present invention.

FIG. 13 is an expanded version of FIG. 12, showing the time span from 5hrs to 25 hrs in greater detail, according to an embodiment of thepresent invention.

FIG. 14 is a graph of hydrocarbon concentration versus time for fivepurge gas mixtures exiting the wafer chamber of FIG. 5, with a siliconwafer in the chamber, the purge gases containing 0%, 0.001%, 0.01%,0.1%, and 1.0% oxygen, according to an embodiment of the presentinvention.

FIG. 15 is an expanded version of FIG. 14, showing the time span from 10hrs to 24 hrs in greater detail, according to an embodiment of thepresent invention.

FIG. 16 is a graph of the time required to reduce ethyl benzene levelsto 10 ppt using either N₂ or XCDA at various temperatures.

FIG. 17 is a graph of the time required to reduce meta- and para-xylenelevels to 10 ppt using either N₂ or XCDA at various temperatures.

FIG. 18 is a graph of the time required to reduce ortho-xylene levels to10 ppt using either N₂ or XCDA at various temperatures.

FIG. 19 is a graph of the time required to reduce ethyl benzene levelsto 10 ppt at various oxygen concentrations.

FIG. 20 is a graph of the time required to reduce meta- and para-xylenelevels to 10 ppt at various oxygen concentrations.

FIG. 21 is a graph of the time required to reduce ortho-xylene levels to10 ppt at various oxygen concentrations.

FIG. 22 is a schematic flow diagram for the wet gas purging experimentdescribed in Example 5.

FIG. 23 is a graph of ethylbenzene concentration versus time for fourpurge gas mixtures exiting the wafer chamber of FIG. 5, the purge gasescontaining 20% oxygen in nitrogen, 100% nitrogen, 0.5% water in nitrogenand 100 ppm water in nitrogen.

FIG. 24 is a graph of combined ortho-xylene concentration versus timefor four purge gas mixtures exiting the wafer chamber of FIG. 5, thepurge gases containing 20% oxygen in nitrogen, 100% nitrogen, 0.5% waterin nitrogen and 100 ppm water in nitrogen.

FIG. 25 is a graph of meta and para-xylene versus time for four purgegas mixtures exiting the wafer chamber of FIG. 5, the purge gasescontaining 20% oxygen in nitrogen, 100% nitrogen, 0.5% water in nitrogenand 100 ppm water in nitrogen.

FIG. 26 is a graph of the time required to ethyl benzene levels to 10ppt using various moisture concentrations in either N₂ or XCDA.

FIG. 27 is a graph of the time required to meta- and para-xylene levelsto 10 ppt using various moisture concentrations in either N₂ or XCDA.

FIG. 28 is a graph of the time required to ortho-xylene levels to 10 pptusing various moisture concentrations in either N₂ or XCDA.

FIG. 29 is a schematic flow diagram of the testing setup according to anembodiment of the invention.

FIG. 30 is a chromatograph of typical valve outgassing immediately afterinstallation.

FIG. 31 is a chromatograph of typical valve outgassing at 80° C.

DETAILED DESCRIPTION OF THE INVENTION

Purging of contaminants is required in many applications. For example,the practice of purging UHP components and gas delivery systems in fabshas been common for many years. Purging and cleaning of equipment andsubstrates is also required in a number of other fields including, butnot limited to, microelectronics, aerospace, optics for cleaningequipment such as LCD substrates, nanostructure surfaces, wafers,reticles and optical assemblies. The disclosed methods are generallyapplicable for use in these fields. Historically, highly purifiednitrogen and argon (less than 1 ppb oxygen, water vapor, CO, CO₂, andhydrocarbons) have been used as purge gases during the “dry down” ofthese components. The “dry down” process has been so named because themain purpose of the purging with nitrogen or argon was to removeadsorbed surface impurities such as water and oxygen.

Purge gases are typically inert. Removal of contaminants by a purge gasmay occur by different mechanisms. During the purge process,contaminants diffuse into the purge gas and are carried away in the flowof the gas stream by reaching an equilibrium between the contaminantconcentration in the purge gas and on the surfaces. This requires largevolumes of UHP gases sufficiently clean to absorb contaminants at verylow levels, typically ppb.

Contaminant species adsorbed onto surfaces (e.g., silicon or stainlesssteel) can also be desorbed by a kinetic effect. This takes place when apurge gas at high flow rate bombards the surface and collides with theadsorbed species. Kinetic energy may be transferred during the collisionwhich can lead to desorption. In the above processes, there is nothingto prevent contaminants from readsorbing to the surfaces.

While not being bound by theory, it is believed that the presentinvention provides a new paradigm for purging contaminants fromelectropositive surfaces (e.g., certain plastics, silicon and stainlesssteel). It is proposed that in addition to the kinetic effect, non-inertmolecules such as oxygen and water can exhibit a chemical effect. Thisis where oxygen and water because of their electronegative and polarizednature, respectively, have a strong affinity for the electropositivesurface of the surface and form a weakly bound, absorbed thin layer. Inaddition, the collision of oxygen with a hydrocarbon may lead to apolarized intermediate, in which the hydrocarbon's affinity for a metalsurface is weakened and the hydrocarbon can be more readily be purged.Once a collision leads to desorption, re-adsorption of the contaminantspecies is hindered by the oxygen thin layer. In the case of water,which forms stronger surface bonds, the thin layer is even more rigidand prevents readsorption. Nitrogen is less capable of such protectivebehavior because it is less electronegative than oxygen, and the thinlayer is very weakly bound and less effective. In addition, N₂ islighter than O₂; therefore, it has less of a kinetic effect at the samevelocity. This proposed mechanism is not a limitation of the instantinvention.

In the instant invention, the effective concentration of oxygen can varyover a wide range, as explained below. The nominal concentration of 17to 21% oxygen, corresponding to that found in ordinary air, is includedin this effective concentration range, solving both the issue of costand the asphyxiation hazard.

Furthermore, these oxygen containing purge gas mixtures can be purifiedto a high degree, resulting in contaminant levels in the low ppt range.The purification processes known in the current art (generally forpurifying oxygen) can be applied to the purification of clean dry air(CDA), a common reagent found in most industrial fab plants, or otheroxygen mixtures. Purified air for use in the present invention (i.e.,containing less than about 1 ppb contaminants, particularly less than100 ppt contaminants, such as less than about 10 ppt contaminants, forexample, less than about 1 ppt contaminants) will be referred to as XCDA(extra clean dry air, XCDA is a registered trademark of MykrolisCorporation) to clearly distinguish it from CDA, a term commonly used inthe art to refer to air with up to 100 ppm contaminant, typically 10-20ppm contaminant. Purifiers for the preparation of XCDA are manufactured,for example, by Aeronex, Inc., of San Diego, Calif. (e.g., the OPTICS™Gas Purifier Series of GateKeeper® purifiers; particularly theO-series), now part of Mykrolis Corporation of Billerica, Mass. Methodsfor preparation of oxygen and oxygen containing gases to sufficientlevels of purity are well known to those skilled in the art (e.g., seeU.S. Pat. No. 6,391,090, incorporated herein by reference). Use of apurifier and in situ purification are not required if a commercialsource of purge gases is sufficiently pure for the intended application.The concentration of contaminants in a purge gas can be measured by asuitably sensitive technique, such as the PAC™ Parts-Per-TrillionAnalyzer Cart marketed by Aeronex. Typically, such techniques involvecollecting contaminants from a gas stream over or within a cold trap foran amount of time sufficient to allow a trace contaminant to accumulateto levels that can be accurately quantified with availableinstrumentation after re-volatilization of the gas.

The oxygen-containing purified gas mixture is comprised of oxygen in aconcentration between 99 volume % and 0.0001 volume %, preferablybetween 25 volume % and 0.1 volume % (e.g., between 25 volume % and 1volume %), and more preferably between 21 volume % and 1.0 volume %.Additionally, the purge gas optionally contains water vapor at 100 ppmto 2 volume %, preferably 100 ppm to 0.5 volume %. The remainder of themixture should be an inert gas chosen from among the group of nitrogen,argon, the noble gases, carbon dioxide, and methane. Preferably,nitrogen should be the major inert component, with all other componentsof the inert gas being present at below about 1 volume %. Preferably,the levels of non-methane hydrocarbons, volatile bases, volatile acids,refractory compounds, and volatile metal compounds should be below 1ppb. Preferably, the levels of contaminants should be below 100 ppt,more preferably below 10 ppt, most preferably below 1 ppt. The specificpurification means is well known to those skilled in the art.

The effective concentration of water in the purge gases of the instantinvention, when present, may vary from about 100 ppm to about 2 volume %in the apparatus to be purged, typically no more than 0.5 volume %.Other components of the purge gas (e.g., oxygen, inert gases) are asdescribed immediately above for oxygen-containing purge gases.Theoretically, higher water concentrations can be used; however, it canbe impractical to remove such high concentrations from an apparatusbefore use. Because oxygen and water have been historically consideredimpurities, their use for removal of contaminants is unexpected. Itshall be shown that not only are oxygen and/or water mixtures aseffective as UHP nitrogen for removing hydrocarbons from surfaces, theyactually show improved performance.

The purging methods disclosed herein can be carried out over a widerange of temperatures. Typically, the methods are carried out attemperatures between ambient temperature (about 20° C.) and 50° C.Nevertheless, the methods optionally can be carried out at temperaturesof up to about 100° C. or even 150° C. The temperature is typicallyselected based upon criteria including thermal tolerance of thecomponents to be cleaned, the volatility of the contaminants at varioustemperatures and the temperatures that the components (e.g., siliconwafers) will be subjected to during subsequent steps of themanufacturing process.

FIG. 4 is a schematic flow diagram of a testing setup according to anembodiment of the present invention. A double dilution system 100 asdescribed previously is utilized to create known hydrocarbonconcentrations from gas standard 114. Concentration curves for othercontaminants can be similarly established using methods well known tothose skilled in the art. Nitrogen, XCDA, or other oxygen containingmixtures are fed to the carrier input 102. When producing a hydrocarbonmixture to contaminate the surfaces of a test device, nitrogen is chosenat input 102, the hydrocarbon component concentrations being determinedby mass flow controllers 108-110 and the concentration of hydrocarbonsin gas standard 114. When the purging performance of the purge gas isbeing evaluated, either nitrogen or a mixture of nitrogen and oxygen arechosen at input 102, with valve 109 closed and valves 107 and/or 111open. Purifier 104 purifies the nitrogen or nitrogen-oxygen mixtures.The gas mixtures created by system 100 are directed to the device undertest (DUT) 402. The hydrocarbon concentrations leaving the DUT 402 areintroduced into the input 122 of the gas chromatograph gas analysissystem 400, where the hydrocarbon levels can be measured, as previouslydescribed and known to those skilled in the art.

Generally, the purging effectiveness of the oxygen mixtures wasdetermined by first purging a test device with a hydrocarbon mixture innitrogen to saturate the surfaces with hydrocarbons, then removing thehydrocarbons in the gas, and continuing the purging process with eitherUHP nitrogen or purified oxygen mixtures, and measuring the hydrocarbonconcentrations in the gas leaving the DUT. The faster the hydrocarbonconcentration drops in the gas exiting the DUT, the more effective thepurging process.

FIG. 5 is a cross section schematic view of a wafer chamber 500according to an embodiment of the present invention. The wafer chamberis used to evaluate the effectiveness of purging hydrocarbons fromstainless steel and silicon surfaces. The chamber has an inlet port 506,an outlet port 508, and supports 512 to hold 100 mm diameter siliconsubstrate 510 in the purge gas environment. The internal surfaces of thewafer chamber are electropolished 316 stainless steel. The wafer chamberdiameter D (ref 502) was 6.0 inches, having a height dimension H (ref504) of 3.9 inches. Wafer chamber 500 was connected as the DUT 402 inthe system shown in FIG. 4.

FIG. 6 is a process block diagram 1900 of a first purging processaccording to an embodiment of the present invention. The process beginswith step 1902, wherein a purge gas mixture containing oxygen ispurified. Moisture, when added, is typically added to the oxygencontaining gas mixture after purification with step 1928 by passagethrough a humidifying device 1930. Alternatively, the purge gas containsmoisture, but no oxygen. Moisture may be added by any method known tothose skilled in the art (e.g., a bubbler). However, methods that allowcareful control of the amount of moisture added are preferred. A numberof types of calibrated tubing with defined water permeabilities areknown to those skilled in the art and are commercially available. Tubesare made of nylon, silicon, Teflon® (poly(ethylene tetrafluoride); PTFE)and Nafion® (Dupont). The purified purge gas is passed through a chamberthrough which the tubing containing ultrapure water (less than 1 ppbcontaminants) runs. The amount of moisture entering the purified purgegas can be determined for a specific flow rate of both water and purgegas. Such methods are well known to those skilled in the art. Thehumidified purge gas is delivered to the device in step 1932.

In step 1904, the purified purge gas containing oxygen and/or water isfed to the device to be purged. Optionally, the device may be heated instep 1908 to reduce the purge time. If heating is employed, the processproceeds along paths 1906 and 1910 to step 1912. In step 1912, a portionof the internal surfaces are contacted with the oxygen and/or watercontaining purge gas. In step 1914, a portion of the contaminantspresent on the internal surfaces of the device are transferred to thepurge gas, creating a contaminated purge gas. Surfaces contained withinthe device being purged may be metal, metal oxides, intermetallics,silicon, silicon oxides, ceramics, nitrides and/or plastics. Preferably,the surfaces are electropolished stainless steel, silicon, and oxides ofsilicon. Also in step 1914, the contaminated purge gas is removed fromthe device. In step 1916, the purging process is continued until thecontaminant concentration in the purge gas is below a predeterminedlimit. This limit may be less than 1 ppb, preferably less than 100 ppt,more preferably less than 10 ppt, most preferably less than 1 ppt. In apreferred optional step 1918, an oxygen and water containing purge gasor water containing purge gas is removed by purging with a dry gasincluding oxygen, nitrogen or other inert gas to remove the water, whichis incompatible with a number of high purity applications. In anotherpreferred optional step 1918, an oxygen containing purge gas is removedby purging with nitrogen or another inert gas, if the device is to beplaced into service where oxygen is considered undesirable. Theseoptional steps 1918 are preferably conducted while the device is heated.If the device was heated, the device should be cooled in step 1922 andreturned to service in step 1926 via paths 1920 and 1924.

FIG. 7 is a process block diagram 2000 of a second purging processaccording to an embodiment of the present invention. The process beginswith step 2002, wherein a purge gas mixture containing oxygen ispurified. The requirements for the inert gas are as described above.Purification means to obtain such high purity gases are well known tothose skilled in the art. In step 2004, the purified purge gascontaining oxygen is optionally fed, in step 2030, to a humidifyingdevice 2032 and returned in step 2034 to be fed to the device to bepurged. Alternatively, the purified purge gas is humified, but containsno oxygen. Optionally, the device may be heated in step 2008 to reducethe purge time. If heating is employed, the process proceeds along paths2006 and 2010 to step 2012. In step 2012, a portion of the internalsurfaces are contacted with the oxygen and/or water containing purgegas. In step 2016, a portion of the contaminants present on the internalsurfaces of the device are transferred to the purge gas, creating acontaminated purge gas. Surfaces contained within the device beingpurged can be metal, metal oxides, intermetallics, silicon, siliconoxides, ceramics, nitrides and/or plastics. Preferably, the surfaces areelectropolished stainless steel, silicon, and oxides of silicon. Also instep 2016, the contaminated purge gas is removed from the device. Instep 2018, the purging process is continued for a predetermined timeperiod. This may be more convenient than basing the purge time on themeasurement of contaminant concentration, which requires complex andsensitive analytical equipment. In a preferred optional step 2020, anoxygen and water containing purge gas or water containing purge gas isremoved by purging with a dry gas including oxygen, nitrogen or otherinert gas to remove the water. If the device is to be placed intoservice where oxygen is considered undesirable, nitrogen or inert gasshould be used for the post-cleaning purge. If the device was heated,the device should be cooled in step 2024 and returned to service in step2028 via paths 2022 and 2026.

FIG. 8 is a process block diagram 2100 of a third purging processaccording to an embodiment of the present invention. In step 2102, aninert gas is supplied. The requirements for the inert gas are asdescribed above. In step 2104, the inert gas is purified via a processor processes well known to those skilled in the art. In step 2106,essentially pure oxygen or a mixture containing oxygen is supplied. Instep 2108, the oxygen or oxygen mixture is purified via a process orprocesses that are well known to those skilled in the art. In step 2110,the purified oxygen or oxygen mixture from step 2108 is combined withthe purified inert gas from step 2104. Optionally, the purificationstages may be performed after the combining of the gases in step 2110.After step 2110, the purified purge gas containing oxygen is optionallyfed, in step 2136, to a humidifying device 2138 and returned in step2140, so that the purified purge gas containing oxygen and/or water isfed to the device to be purged. Optionally, the device is heated in step2116 to reduce the purge time. If heating is employed, the processproceeds along paths 2114 and 2118 to step 2120. In step 2120, a portionof the internal surfaces are contacted with the oxygen containing purgegas. In step 2122, a portion of the contaminants (e.g., hydrocarbons)present on the internal surfaces of the device are transferred to thepurge gas, creating a contaminated purge gas. Surfaces contained withinthe device being purged may be metal, metal oxides, intermetallics,silicon, silicon oxides, ceramics, nitrides and/or plastics. Preferably,the surfaces are electropolished stainless steel, silicon, and oxides ofsilicon. Also in step 2122, the hydrocarbon purge gas is removed fromthe device. In step 2124, the purging process is continued for apredetermined time period, or to a predetermined hydrocarbon level. Thislevel is typically less than 100 ppt, but is preferably less than 10ppt. In a preferred optional step 2126, the oxygen and water containingpurge gas is removed by purging with a dry gas including oxygen,nitrogen or other inert gas to remove the water. If the device is to beplaced into service where oxygen is considered undesirable, nitrogen orinert gas should be used for the post-cleaning purge. If the device washeated, the device should be cooled in step 2130 and returned to servicein step 2134 via paths 2128 and 2132.

EXAMPLE 1

The effectiveness of removing hydrocarbons from 316 stainless steelelectropolished surfaces with oxygen mixtures is demonstrated in thisexample. 316 stainless steel electropolished surfaces are widely used inUBP gas distribution systems in mass flow controllers, pressureregulators, and interconnecting pipe and tubing. They are also widelyused as a process chamber material in semiconductor manufacturingequipment. An empty (no silicon wafer 510 present) wafer chamber 500,was first purged with a nitrogen-hydrocarbon mixture containingapproximately 10 ppb each of benzene, toluene, ethyl-benzene, meta- andpara-xylene, and ortho-xylene for approximately 3.5 hours. Following thehydrocarbon exposure, the wafer chamber was purged with UHP nitrogen andthe hydrocarbon concentrations in the purge gas exiting the chamber weremeasured. The hydrocarbon exposure was then repeated. Following thesecond hydrocarbon exposure, the wafer chamber was purged with purifiedXCDA, which contained approximately 20% oxygen by volume.

FIG. 9 is a graph 600 of hydrocarbon concentration 604 versus time 602for two purge gas mixtures exiting the wafer chamber of FIG. 5, with nowafer in the chamber, according to an embodiment of the presentinvention. Broken curve 606 shows the total concentration decay responseof all six hydrocarbons in the purge gas leaving the wafer chamber witha pure nitrogen purge gas. Solid curve 608 shows the total concentrationdecay response of all six hydrocarbons in the purge gas leaving thewafer chamber with a purified XCDA purge gas. Ref 610 indicates thepoint where the hydrocarbon containing purge gas was substituted withthe nitrogen or XCDA.

The elution times of the hydrocarbons in curves 606 and 608 werecompared to the time it would take to dilute the original 60 ppbhydrocarbon concentration to 10 ppt, given the wafer chamber volume ofapproximately 1.5 liters and purge flow rate of 0.75 liters/min. For auniformly mixed system, it would take about 8.7 time constants to reducean initial 60 ppb concentration to 10 ppt. The time constant is definedas the wafer chamber volume divided by the purge flow rate. At a timeconstant of approximately two minutes, simple dilution would take under20 minutes to reach 10 ppt from an initial starting point of 60 ppb. Theactual time for either the XCDA or pure nitrogen to reach 10 ppt isconsiderably longer, indicating that removal from the internal stainlesssteel surfaces is dominating the hydrocarbon elution from the waferchamber. Other tests have shown that once the hydrocarbons are reducedto very low levels (10 ppt and below) by purified XCDA, subsequentpurging by UHP nitrogen does not produce hydrocarbon concentrationsabove the levels last obtained with the XCDA.

EXAMPLE 2

In this example, the test described in Example 1 was repeated, with theexception that a bare 100 mm (4 inch) silicon substrate 510 was placedin the wafer chamber 500 prior to exposure to the nitrogen-hydrocarbonmixture. FIG. 10 is a graph 700 of total hydrocarbon concentration 704versus time 702 for two purge gas mixtures exiting the wafer chamber ofFIG. 5, with a silicon wafer in the chamber, according to an embodimentof the present invention. Curve 706 shows the decay in hydrocarbonconcentration while the wafer chamber and wafer are purged with UHPnitrogen. Curve 708 shows the decay in hydrocarbon concentration whilethe wafer chamber and wafer are purged with purified XCDA. Ref 710indicates the approximate point where feed of nitrogen-hydrocarbonmixture was terminated. Curves 706 and 708 clearly indicate hydrocarbonremoval from silicon substrates is significantly slower than thestainless steel surfaces of the wafer chamber. As in the previousExample 1, the oxygen containing purge gas (curve 708) shows a morerapid reduction in hydrocarbon concentration, when compared to UHPnitrogen (curve 706). FIG. 11 is an expanded version of FIG. 10, showingthe time span from 10 hrs to 25 hrs in greater detail. Here it can bemore clearly seen from graph 800 that hydrocarbon concentration 804versus time 802 for the XCDA purge (curve 808) is in advance of the UHPnitrogen curve 806. At the 20 ppt concentration level, the UHP nitrogenresponse lags the XCDA response by nearly 5 hours. This, of course,means that it would require 5 hours longer to purge the wafer chamberand wafer to the 20 ppt level with UHP nitrogen.

EXAMPLE 3

FIG. 12 is a graph 900 of meta- and para-xylene concentration 904 versustime 902 for three purge gas mixtures exiting the wafer chamber of FIG.5, with a silicon wafer in the chamber, the purge gases containing 0%,1%, and 20% oxygen, according to an embodiment of the present invention.In this example, 1% oxygen and 20% oxygen (in nitrogen) are compared toUBP nitrogen. The hydrocarbon mixture used was approximately 10 ppb ofmeta-xylene and 10 ppb of para-xylene in nitrogen. As in Example 2, asilicon substrate was placed in the wafer chamber prior to thehydrocarbon exposure. Curve 906 in FIG. 12 shows the concentrationresponse of both xylenes as a function of time during a UHP nitrogenpurge. Curve 908 shows the concentration response of both xylenes as afunction of time during a 1% oxygen (by volume) in nitrogen purge. Curve910 shows the concentration response of both xylenes as a function oftime during a 20% oxygen (by volume) in nitrogen (XCDA) purge. Ref 912indicates the point at which the hydrocarbon feed gas was terminated.FIG. 13 is an expanded version of FIG. 12, showing the time span from 5hrs to 25 hrs in greater detail. Here it can be more clearly seen fromgraph 1000 that hydrocarbon concentration 1004 versus time 1002 for the1% oxygen purge gas (curve 1008) and the 20% oxygen purge gas (curve1010) is in advance of the UHP nitrogen curve 1006. From a comparison ofthe three curves 1006-1010, it can be noted that 1% oxygen is aseffective as 20% for hydrocarbon levels above 10 ppt, but that thehigher oxygen concentration has a slight advantage at levels below 10ppt. Both oxygen containing purge gases demonstrate a significantadvantage over purging with UHP nitrogen.

EXAMPLE 4

20 FIG. 14 is a graph 1100 of hydrocarbon concentration 1104 versus time1102 for five purge gas mixtures exiting the wafer chamber of FIG. 5,with a silicon wafer in the chamber, the purge gases containing 0%,0.0001%, 0.01%, 0.1%, and 1.0% oxygen, according to an embodiment of thepresent invention. The hydrocarbon-nitrogen contamination mixture was 60ppb total hydrocarbon concentration, as described in Example 1. Datarepresenting the purge response of UHP nitrogen (ref 1106, curve 1116),0.0001% oxygen (by volume) in nitrogen 1108, 0.01% oxygen (by volume) innitrogen 1110, 0.1% oxygen (by volume) in nitrogen 1112, and 1% oxygen(by volume) in nitrogen (ref 1114, curve 1118) are plotted in graph1100. All the data fall between the 0% oxygen curve 1116 (UHP nitrogen)and the 1% oxygen curve 1118, as might be expected. Purgingeffectiveness increases as oxygen concentration increases within theranges of oxygen concentration shown. FIG. 15 is an expanded version ofFIG. 14, showing the time span from 10 hrs to 24 hrs in greater detail.The graph 1200 of hydrocarbon concentration 1204 versus time 1202 isplotted with data representing the purge response of UHP nitrogen (ref1206, curve 1216), 0.0001% oxygen 1208, 0.01% oxygen 1210, 0.1% oxygen1212, and 1% (ref 1214, curve 1218). See FIGS. 16-21 which show dry-downtimes versus temperature or concentration.

EXAMPLE 5

The effectiveness of removing hydrocarbons from 316 stainless steelelectropolished surfaces with water mixtures is demonstrated in thisexample using a method similar to that in Example 1. See FIG. 22.Initially purified nitrogen gas was mixed with a six-componenthydrocarbon gas standard (benzene, toluene, ethylbenzene, xylenes; BTEX)to create a known challenge of 60 ppb total organic compounds (TOC). Thewafer chamber, housing a wafer, was purged with the challenge gas understandard operating conditions of 0.75 slm, 30 psig and ambienttemperature. The wafer chamber effluent was measured for hydrocarbonlevel using a gas chromatograph with a flame ionization detector untilits concentration reached 60 ppb±2 ppb hydrocarbon. The stabilizationtime for the chamber to condition occurred after 4-5 hours.

After the wafer chamber was saturated with the 60 ppb TOC, the BTEXchallenge was turned off and moisture or oxygen was added to thenitrogen gas stream as indicated. The wafer chamber effluent wasmonitored until its TOC concentration dried down below the 10 ppt levelfor each contaminant.

FIG. 23 is a graph 1600 of time 1602 versus ethylbenzene concentration1604 for four purge gas mixtures exiting the wafer chamber of FIG. 5,the purge gases containing 100% nitrogen, 20% oxygen, 0.5% water and 100ppm water according to an embodiment of the present invention. Thehydrocarbon-nitrogen contamination mixture was 60 ppb total hydrocarbonconcentration, as described in Example 1. Data representing the purgeresponse of ethylbenzene to UHP nitrogen 1606, 20% oxygen (by volume) innitrogen 1608, 100 ppm water (by volume) in nitrogen 1610 and 0.5% water(by volume) in nitrogen 1612 are plotted in graph 1600. Purgingeffectiveness increases as water concentration increases within theranges of water concentration shown.

FIG. 24 is a graph 1700 of time 1702 versus ortho-xylene concentration1704 for four purge gas mixtures exiting the wafer chamber of FIG. 5,the purge gases containing 100% nitrogen, 20% oxygen, 0.5% water and 100ppm water according to an embodiment of the present invention. Thehydrocarbon-nitrogen contamination mixture was 60 ppb total hydrocarbonconcentration, as described in Example 1. Data representing the purgeresponse of ortho-xylene to UHP nitrogen 1706, 20% oxygen (by volume) innitrogen 1708, 100 ppm water (by volume) in nitrogen 1710 and 0.5% water(by volume) in nitrogen 1712 are plotted in graph 1700. Purgingeffectiveness increases as water concentration increases within theranges of water concentration shown.

FIG. 25 is a graph 1800 of time 1802 versus para- and meta-xylene 1804for four purge gas mixtures exiting the wafer chamber of FIG. 5, thepurge gases containing 100% nitrogen, 20% oxygen, 0.5% water and 100 ppmwater according to an embodiment of the present invention. Thehydrocarbon-nitrogen contamination mixture was 60 ppb total hydrocarbonconcentration, as described in Example 1. Data representing the purgeresponse of para- and meta-xylene to UHP nitrogen 1806, 20% oxygen (byvolume) in nitrogen 1808, 100 ppm water (by volume) in nitrogen 1810 and0.5% water (by volume) in nitrogen 1812 are plotted in graph 1600.Purging effectiveness increases as water concentration increases withinthe ranges of water concentration shown. TABLE 1 Reduction in Dry DownTime Using Moisture Dry-Down Times Diffence(Hr) Ethyl- m,p- o- Purge GasCompared benzene Xylene Xylene Dry N2 and 0.1% H2O in N2 5.03 9.60 7.57Dry N2 and 0.5% H2O in N2 6.37 12.25 9.57 Dry XCDA and 0.1% H2O in XCDA2.23 5.42 4.83 Dry XCDA and 0.5% H2O in XCDA 3.70 6.93 4.93See FIGS. 26-28 which show dry-down times versus temperature orconcentration.

EXAMPLE 6

In a comparative test to determine the efficacy of XCDA as compared tonitrogen for decontamination of UHP equipment, a quantitativemeasurement system was assembled incorporating three commercial UHPdiaphragm valves, each from a different manufacturer. The setup is shownin FIG. 29, 1300. To perform outgassing tests, each valve under test1302, VUT, was connected directly upstream of the cold trap 1304 asshown. Purified sample gas (N₂ or XCDA) was sent through each VUT with agas purity specification of less than 1 ppt hydrocarbon. The supply N₂and XCDA were purified with an inert purifier (Aeronex, SS-500KF-I-4R)and optics purifier (Aeronex, SS-700KF-O-4R), respectively. A heatertape and temperature probe were wrapped around the VUT to heat andmonitor the temperature (not shown). As the gas purged through the VUT,any desorbed contaminants were collected downstream in the cold trap forhydrocarbon analysis in the gas chromatogram 1304.

Valves were selected as representative of UHP system contaminationsources since prior investigations had shown evidence of hydrocarboncontamination being generated by outgassing from elastomeric componentsin the valves. Detection and measurement was by means of cold trapcollection and gas chromatographic measurement. The size of thecontaminants was determined by retention time on the column (TOC) ascompared to known standards. Chromatographs 1400 and 1500 showing timein minutes 1402 and 1502 versus m Volts 1404 and 1504, respectively fromthe outgassing of valves at two different temperatures, ambient andabout 80° C., are shown in FIGS. 30 and 31. A rough analysis of the sizeof the contaminants based on the chromatographs is presented in Table 2below. TABLE 2 Analysis of contaminants by Total Organic Contaminants(TOC) by GC/FID Time Compound % outgassing <10 min <5 carbons 10-20%10-16 min 6-10 carbons 0-5% 16-25 min 11-15 carbons 20-40% >25 min >15carbons 50-80%

It should be noted that the majority of the contaminants released arehigh molecular weight contaminants. This is in contrast to the priorexamples where purging of low molecular weight hydrocarbons (i.e., lessthan 8 carbons) was analyzed.

Measurements were made at 0 and 60 minutes of system operation atambient temperature (approximately 20° C.) and at 0, 60 and 720 minutesat 80° C. Measurements were made of both one-pass and two-pass purges bythe different gases. In each case a nitrogen purge was followed by anXCDA purge. In the two-pass test the XCDA purge was followed by a secondnitrogen purge. Tests of the three different UHP valves produced threedifferent results. One valve started out with a low level of hydrocarbonoutgassing and did not exceed 100 ppt even during elevated thermal XCDAtesting, while another produced temperature sensitive contaminationresults. The remaining valve started out at 100 and peaked at 1000 ppt.On the positive side all valves through proper purging and thermalcycling were able to achieve levels at or below the 1 ppt lower limit ofthe detection capability of our test instruments. This indicates thatthrough proper preconditioning any of these valves could be used in UHPpiping system to deliver 1 ppt gas to the process. Results for the valveproducing the 100-1000 ppt outgassing were as shown below in Table 3.TABLE 3 Nitrogen vs. XCDA Purging of UHP Valves Time TemperatureNitrogen XCDA No. of Passes (minutes) (° C.) (ppt) (ppt) 1 0 Ambient 10050 1 60 Ambient 180 50 1 0 80 1000 40 1 60 80 700 100 1 720 80 12 0 1st2nd 2 (N2) 0 Ambient 100 0 50 2 (N2) 60 Ambient 180 0 50 2 (N2) 0 801000 0 40 2 (N2) 60 80 700 0 100 2 (N2) 720 80 12 0 0

It will be evident from the data of Table 3 that over all of thetemperature and time ranges, purges with nitrogen produced only limitedand quite unacceptable reductions of the hydrocarbon contamination ofthe valve. The subsequent purge with the XCDA reduced the hydrocarboncontaminant level to much lower levels, bettering the nitrogen purgelower limit by factors of 2-25. Further the XCDA purges to the lowlevels occurred in very short times as compared to the time required forthe nitrogen purges to effect significant reductions. (The increasesseen for the first nitrogen purge at ambient temperature and the XCDApurge at 80° C. between 0 and 60 minutes are believed to be due to thetime required for some hydrocarbon contaminants within the elastomericcomponents to migrate to the surface for purging. This is a physicalphenomenon of the elastomeric materials of the valve and notrepresentative of the purge capabilities of the respective gases.)

The generally accepted protocol for UHP gas line validation requiresextensive purging with nitrogen followed by verification that the lineis contaminant free in a nitrogen purge environment. However, with allthe valves XCDA volatilized additional hydrocarbons which remain afterUHP nitrogen cleaning and thermal cycling. Even at ambient temperature,additional hydrocarbons were released when exposed to an oxygen richpurge gas.

A second series of tests were conducted to determine any effect from theorder in which the purge gases were used. Two equivalent commercialvalves from the same manufacturer were tested for hydrocarbondecontamination. One (A1) was purged with nitrogen followed by XCDA, andthe other (A2) with XCDA followed by nitrogen. The results are presentedin Table 4 below: TABLE 4 Nitrogen/XCDA Purge vs. XCDA/Nitrogen PurgeValve A1 Valve A2 Time Temperature N2 XCDA XCDA N2 (minutes) (° C.)(ppt) (ppt) (ppt) (ppt) 0 ambient 50 50 50 90 60 ambient 10 190 19 9 080 220 220 510 2 60 80 200 100 35 2 720 80 10 5 0 0

The XCDA step at ambient temperature produced results similar to thenitrogen purge. However, when Valve A2 was heated to 80° C. under XCDApurge, the hydrocarbon outgassing rate increased significantly and thendropped quickly to below the limits of the detection equipment.Repeating the test in nitrogen showed little improvement. When purgingwith nitrogen, UHP components produced a continuous release ofhydrocarbons. Actual peak values often did not occur until long afterthe initiation of purging due to the slow migration of heavierhydrocarbons through the piping system.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A method for the removal of airborne molecular contaminants (AMC)from a substrate, comprising: contacting at least a portion of thesubstrate with a purified purge gas, the purified purge gas comprisingoxygen and water, and the purified purge gas having an AMC concentrationless than about 1 part per billion (ppb) on a volume basis, thesubstrate contaminated with AMC before the substrate is contacted withpurified purge gas; producing a contaminated purge gas by transferring aportion of the contaminants from the substrate into the purified purgegas; and removing the contaminated purge gas from the substrate, therebyremoving AMC from the substrate.
 2. (canceled)
 3. The method of claim 1,wherein the method is repeated until the contaminated purge gas has anAMC concentration below about 1 ppb AMC on a volume basis.
 4. The methodof claim 1, wherein the AMC concentration of the purified purge gas isless than about 100 parts per trillion (ppt) on a volume basis.
 5. Themethod of claim 1, wherein the purified purge gas is less than about 10ppt on a volume basis.
 6. The method of claim 1, wherein the AMCconcentration of the purified purge gas is less than about 1 ppt on avolume basis.
 7. (canceled)
 8. The method of claim 1, wherein the watercomprises at least about 100 parts per million (ppm) by volume of thepurified purge gas.
 9. The method of claim 8, wherein the watercomprises about 100 ppm to about 0.5% by volume of the purified purgegas.
 10. (canceled)
 11. The method of claim 1, wherein the deviceencloses substrate comprises at least one silicon substrate.
 12. Themethod of claim 1, wherein the substrate is an interior surface of anultrahigh purity gas line component.
 13. The method of claim 1, whereinthe substrate is the interior surface of a valve.
 14. The method ofclaim 1, further comprising purging the substrate with an inert gas toremove at least one of oxygen and water after removing the contaminatedpurge gas from the substrate.
 15. The method as of claim 14, wherein theinert gas is selected from the group consisting of nitrogen, argon,noble gases, methane and combinations thereof. 16-35. (canceled)
 36. Themethod of claim 1, wherein the substrate is an electropositive surface.37. The method of claim 1, wherein the substrate is an electropolishedsurface.
 38. The method of claim 1, wherein the substrate is a wafer.39. The method of claim 1, wherein the purified purge gas is inert withrespect to the AMC.
 40. The method of claim 1, wherein the purifiedpurge gas comprises oxygen at a concentration between about 1% and 25%on a volume basis.
 41. The method of claim 1, wherein the purified purgegas comprises extra clean dry air and water.
 42. The method of claim 1,whereby the method removes AMC from the substrate at a faster rate thanthe method using a purge gas consisting essentially of nitrogen gas. 43.The method of claim 1 further comprising: purifying a purge gas toproduce the purified purge gas for contacting with the substrate. 44.The method of claim 1, wherein the method is performed at a temperatureno higher than about 80° C.
 45. The method of claim 44, wherein themethod is performed at a temperature no higher than about 50° C.
 46. Amethod for the removal of airborne molecular contaminants (AMC) from asubstrate, comprising: contacting at least a portion of the substratewith a purified purge gas, the purified purge gas comprising oxygen andwater, the purified purge gas having an AMC concentration less thanabout 1 part per billion (ppb) on a volume basis; producing acontaminated purge gas by transferring AMC from the substrate into thepurified purge gas; and removing the contaminated purge gas from thesubstrate, wherein the oxygen and water in the purified purge gas are inan amount sufficient to remove AMC from the substrate at a faster ratethan the method using a purge gas consisting essentially of nitrogengas.
 47. The method of claim 46, wherein the method is performed at atemperature no higher than about 80° C.
 48. The method of claim 47,wherein the purified purge gas is inert with respect to the AMC.
 49. Themethod of claim 48, wherein the purified purge gas comprises extra cleandry air and water.